The effect of long exercise training on the indexes of the functional state isolated by Lanhendorf heart of old rats during ischemia-reperfusion, the sensitivity of calciuminduced mitochondrial permeability transition pore (MPTP) opening and the role of NO-dependent mechanisms of poreformation regulatory were investigated. Thus, reperfusion injury of the heart contractile function and its myocardial oxygen metabolism were less pronounced in old rats adapted to exercise long training pointing for its positive effect. It is shown a decreased sensitivity of MPTP to its inductor Ca2+ in the heart of old trained rats due to an increase by 1.5-2 orders in threshold Ca2+ concentration, which induces swelling of organelles. At the same time, in heart mitochondria of trained adult rats we observed almost doubled activity of constitutive NO-synthase (cNOS) compared with control (6,02 Ѓ} 0,08 and 3,64 Ѓ} 0,27 pmol / min * mg protein, respectively (P.0,05 )) and a slight increase in the activity of inducible NO-synthase (iNOS). Regulation of pore formation in older animals trained was performed by a significant decreased iNOS activity compared with control aged rats (12,29 Ѓ} 3,11 and 9,25 Ѓ} 1,24 pmol/min*mg protein, respectively (P.0,05)) on the background slight increased in cNOS activity. We hypothesized that a decrease in sensitivity of the MPTP-opening occurred due to an increased production of NO pointing to its role as an inhibitor of pore formation during exercise. It has been shown to increase the sensitivity of MPTP to Ca2+ in the heart under the conditions of reduce the NO production by a single injection of NO syhnthase inhibitor N(omega)-nitro- L-arginine methyl ester (L-NAME) in dose of 10 mg/kg to trained animals of all ages. Using real-time polymerase chain reaction we showed that the gene expression of eNOS in the heart was significantly greater than that of nNOS and iNOS. Thus, in the heart of adult trained rats the expression of mRNA nNOS were increased 5 times, mRNA iNOS - 24 times (P <0,05), and the gene expression of eNOS decreased 3.5 times compared with untrained rats. In the heart of old trained rats the expression of nNOS mRNA decreased 4 times (P<0,05) and iNOS mRNA - 2 times compared with the old untrained animals. In heart of old trained rats we observed a workout recovery of eNOS mRNA expression to the values of control adult animals. Taken together, our data suggest that a longterm exercise training improves functional state of the heart during aging and increases the resistance of body to oxidative stress under reperfusion injury due to a decreased sensitivity of MPTP to Ca2+ and increased activity of mitochondrial cNOS.